I don't have a lot of experience with IEM's, so these impressions are in comparison to full size headphones and speakers.  Not sure if that matters.  I tried all the Shure included tips but no aftermarket ones. 

Overall
I would generally describe the SE535 as a headphone that doesn't sound bothersome, but doesn't really impress either.  Similar to the veiled LCD-3 only not as good.  I can live with them, and enjoy music with them, but I'm not that excited about them.  They have an FR similar to the LCD-2 except with less bass, but they have different tonalities.  The 535 has LCD-2 like treble except one spot of exaggeration which causes some sibilance. 

Pros
fairly balanced FR
no resonances, or less than almost all headphones (to my ears)
tonality is good, but not outstanding
nothing terribly bothersome

Treble
One of their weakest areas.  It's not harsh, or painful, or pronounced/exaggerated which makes it better than a lot of headphones and very listenable for me.  But the treble is a little rough sounding, has texture that shouldn't be there, can sound kind of tinny, and at times sibilant though again, it's not sharp or peircing or harsh.  It's also rolled off, with not enough air which is a bad combo to have with sibilance.  I'm guessing the FR is a bit uneven in the treble with at least one peak followed by roll off, but that's just a guess based on what I've gathered from similar problems in other phones.  It's not that bad, it can be ignored unless you're a treble head.  But stax have much much better treble.  As well as many dynamic headphones.  I'd say the HD650 has better treble by having a smoother, more even presentation that's better integrated with the midrange and with no sibilance.  But a lot of headphones have much worse treble in that it's painful. 

Mids and Bass
I lump them together because that's how they sound to me in this phone.  They're coherent from bass to mids, you don't wind up thinking "bass + midrange" and they have the same strengths and weaknesses.  They are both pretty good, and seem neutral, nothing sticks out or seems recessed until possibly the upper mids where they may start to roll off (I'm not sure on this one because I'm not sure if I'm good at hearing recession in the upper mids, I'm suspicious it may not bother me), so the SE535 aren't bothersome in this range at all which again, puts them above most headphones on that alone- there's no upper midrange emphasis, glare, shout or any such thing which is incredibly rare and quite an achievement IMO.  Bass extends plenty low, and sounds netural-ish, erring on the side of being a bit bass lite, and lacking in weight, but they have enough.  Bass is not outstanding in terms of detail or control, but it gets the job done and is never in the way.   However, they aren't that transparent in the mids to bass.

Cons
Something about them keeps reminding me of a noisy photograph with too much smoothing noise reduction.  It's hard to describe, but it sounds like there's an oversmoothed surface glossing over a rough, edgy interior.  So the smoothing takes care of any gross, easily apparent problems and makes the general picture a good one, but when you listen closer, both the edgy roughness, and the smoothing ruins subtlties like fine details and dynamics and proper tonality.  Vocals don't sound bad, but they lack realism, transparency, and sound like they're hazed over somehow.  Really, it's the same drawbacks as with a digital image taken at very high iso, despite smoothing making it usable, it will never have the f inesse of an image taken at lower iso.  It's as if the sonic picture is made up of large chunks of smoothed information instead of lots of little details.  Sounds like a fake smoothness, rather than one that comes from speed and accuracy. 

Conclusion
Good headphone.  Not outstanding.  I can certainly live with mine, I don't use them that often.  No major problems esp in the midrange which is what makes them livable, except for the sibilance which is probably the only gross problem.  If I was using IEM's all the time, I'd want something with more transparency and better treble.  I'm sure there are lots of IEM's with better treble, but I wonder how many of them wouldn't have some rather serious issues that the 535 doesn't have.  I don't know IEM's well enough to say.  I could live with the rough treble and strange oversmoothed effect better than I could live with sharp painful peaks or resonance.